Clinical goal treatment planning and optimization

ABSTRACT

An apparatus for developing an intensity-modulated radiation therapy treatment plan includes a memory that stores machine instructions and a processor that executes the machine instructions to receive a clinical goal associated with the treatment plan as a user input. The processor further executes the machine instructions to determine a plan objective based on the clinical goal, generate a cost function comprising a term based on the plan objective, and assign an initial value to a parameter associated with the term. The processor also executes the machine instructions to identify a microstate that results in a reduced value associated with the cost function, evaluate a fulfillment level associated with the clinical goal, and adjust the value of the parameter to improve the fulfillment level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to copending patentapplication Ser. No. 14/866,587, Attorney Docket Number VAR-15-030-US,with a filing date of Sep. 25, 2015, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

This description relates generally to radiation therapy planning, andmore particularly to developing a radiation therapy plan based onclinical goals.

BACKGROUND

Intensity-modulated radiation therapy (IMRT) is an advanced type ofhigh-precision radiotherapy used to deliver precise radiation doses inmedical procedures. IMRT modulates the intensity of multiple radiationfields originating from different directions to primarily focus on aregion of the patient's body that generally conforms to the shape of atarget volume, such as a malignant tumor, while exposing surroundingnormal tissue to reduced levels of radiation. Typically, a detailedtreatment plan is developed using computed tomography (CT) or magneticresonance imaging (MM) of the patient, along with computerized dosecalculations to determine the dose intensity pattern.

In general, IMRT treatment plan optimization processes have been basedon a cost function, which scores the achieved dose distribution. Thecost function generally is defined such that more desirable treatmentplans are associated with a microstate that results in relativelyreduced cost function values. The microstate generally includesparameters needed to deliver the dose to the patient. The cost functiontypically is interactively defined, or specified, by a user, such as amedical technician or a physician, to develop the treatment plan withrespect to certain machine parameters, optimal fluence, or the like.

In a typical optimization process, the user employs a set of treatmentplanning tools to specify the cost function contribution from variousfactors, such as requested target distributions, the dose level oforgans-at-risk (OAR), dose distribution in normal tissue, or the like.In practice, the user generally specifies a set of optimizationobjectives, each of which is correlated with a term of the total costfunction. Optimization objectives include, for example,dose-volume-histogram (DVH) objectives, normal tissue objectives (NTO),and so forth.

Existing treatment plan optimization methodologies can have drawbackswhen used to develop radiation therapy plans. Defining the cost functionto take into account clinical goals can involve a complex, ofteniterative, process requiring significant clinical experience. Ingeneral, the user has limited options with regard to plan improvement.Some plan details, for example, attaining a desired level ofnormalization, can be relatively difficult to control.

In other cases, the clinical goal definitions allow for multipletreatment plans, but it can be difficult to determine which of the plansis dosimetrically superior. In such cases, additional optional goalshave been applied to the plan.

In addition, the dose distribution for multiple regions of normal tissueis controlled by a single NTO, which cannot guarantee achievement ofclinical goals, and related parameters must be manually set by the userto comply with intended clinical goals. As a result, it often can benecessary to define virtual structures, that is, specified spatialregions having no direct anatomical function, in an attempt to controlnormal tissue exposures, for example, in the vicinity of target volumesor near the skin.

SUMMARY

According to one embodiment of the present invention, an apparatus fordeveloping an intensity-modulated radiation therapy treatment planincludes a memory that stores machine instructions and a processor thatexecutes the machine instructions to receive a clinical goal associatedwith the treatment plan as a user input. The processor further executesthe machine instructions to determine a plan objective based on theclinical goal, generate a cost function comprising a term based on theplan objective, and assign an initial estimate of a value of a parameterassociated with the term. The processor also executes the machineinstructions to identify a microstate that results in a reduced valueassociated with the cost function, evaluate a fulfillment levelassociated with the clinical goal, and adjust the value of the parameterto improve the fulfillment level.

According to another embodiment of the present invention, acomputer-implemented method for developing an intensity-modulatedradiation therapy treatment plan includes determining a plan objectivebased on a clinical goal associated with the treatment plan, andgenerating a cost function comprising a term based on the planobjective. The term includes a parameter. The method further includesidentifying a microstate that results in a reduced value associated withthe cost function, evaluating a fulfillment level associated with theclinical goal, and adjusting a value associated with the parameter toimprove the fulfillment level.

According to yet another embodiment of the present invention, a computerprogram product includes a non-transitory, computer-readable storagemedium encoded with instructions adapted to be executed by a processorto implement determining a plan objective based on a clinical goalassociated with the treatment plan, and generating a cost functioncomprising a term based on the plan objective. The term includes aparameter. The instructions are further adapted to implement identifyinga microstate that results in a reduced value associated with the costfunction, evaluating a fulfillment level associated with the clinicalgoal, and adjusting a value associated with the parameter to improve thefulfillment level.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an exemplary intensity-modulatedradiation therapy (IMRT) treatment planning device in accordance with anembodiment of the present invention.

FIG. 2 is a schematic view depicting an exemplary general computingsystem that can implement the treatment planning device of FIG. 1.

FIG. 3 is a flowchart depicting an exemplary method of optimizing anintensity-modulated radiation therapy (IMRT) treatment plan inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

An embodiment of the present invention provides an intensity-modulatedradiation therapy (IMRT) treatment planning device that can be employedby a user, such as a medical technician or a physician, to aid thedevelopment of a therapeutic medical treatment plan, for example, totreat a malignant tumor in a cancer patient. In various embodiments, theIMRT treatment planning device generates a treatment plan solution thatfulfills all of the corresponding clinical goals specified by the user,as many of the user-specified clinical goals as possible, or a subset ofthe user-specified goals in accordance with user-specified priorities.

An embodiment of the IMRT treatment planning device converts clinicalgoals input by the user into plan objectives and creates a cost functionbased on parameters corresponding to the objectives. The IMRT treatmentplanning device iteratively determines an appropriate microstate, ormicroscopic state, that results in a relatively low cost function valueand determines a corresponding treatment plan solution. The treatmentplan solution is generated based on a selected set of machineparameters, such as a selected field geometry, a selected monitor unit(MU) limit, or the like.

In various embodiments, the IMRT treatment planning device receivesclinical goals, for example, regarding the dose distributions withrespect to a target volume, an organ-at-risk (OAR) in the vicinity ofthe target volume, or other specified or unspecified normal tissue, anddevelops a corresponding treatment plan solution. In some embodiments,the IMRT treatment planning device receives residual goals, that is,additional clinical goals that generally may not be fully achieved, butcan be at least partially achieved by the treatment plan solution.

As used in this disclosure, the terms “optimize,” “optimal,”“optimization,” and related terms are used not in a strict sense toindicate an absolute condition, as in the best possible solution, butrather, to imply a relative improvement, a relatively favorablecondition, or a relatively preferable solution. The explicit or implicitmeaning attributed to these terms in any other context should notdetermine the intended meaning or usage herein.

An embodiment of the present invention is shown in FIG. 1, whichillustrates an exemplary intensity-modulated radiation therapy (IMRT)treatment planning device 10 that employs a treatment planmetaoptimization scheme to develop an appropriate IMRT treatment plansolution for a patient. The IMRT treatment planning device 10 includes aclinical goal definition tool 12, an initial plan objective converter14, a cost function generator 16, a state analyzer 18, a dosedistribution evaluator 20, a clinical goal assessor 22, and a parameteradjuster 24.

The clinical goal definition tool 12 receives clinical goal input froman IMRT treatment planning device user, such as a medical technician ora physician. The input clinical goals can include any number of desiredfactors related to treatment outcome, for example, target volume dosedistribution, organ-at-risk dose distributions, other normal tissue dosedistributions, other spatial dose distributions, maximum dose, meandose, minimum dose, or the like. In some embodiments, the input clinicalgoals also include one or more residual goals to be at least partiallyfulfilled, if possible, in addition to attainment of primary clinicalgoals.

In addition, in an embodiment, the clinical goal definition tool 12receives priority input from the IMRT treatment planning device user.For example, the clinical goal definition tool 12 receives a numericrank regarding one or more of the input clinical goals indicating therelative priority of the goals with respect to one another. Thepriorities may indicate, for example, that a particular clinical goal isto be fulfilled, if possible, at the expense of fulfillment of lowerpriority goals. Thus, the input priorities may be used to guide theattempted optimization of the treatment plan.

The initial plan objective converter 14 creates a set of plan objectivesbased on the received clinical goals. In an embodiment, the initial planobjective converter 14 creates a single plan objective corresponding toeach clinical goal. In other embodiments, the initial plan objectiveconverter 14 creates multiple objectives corresponding to one or more ofthe clinical goals. An example plan objective may seek to control a dosedifferential based on a prescription dose and a predicted actual dose ata particular point in a patient volume.

The cost function generator 16 generates a cost function thatincorporates the plan objectives. For example, the cost functiongenerator 16 may design individual cost terms corresponding to the planobjectives, and the value of the cost function may equal the sum of allthe cost terms. Conventionally, the cost function generator 16 designseach of the cost function terms to minimize the value of the costfunction when the corresponding plan objectives, and thus, theassociated clinical goals, are attained.

An example cost term may include a summation or integral of dosedifferentials at multiple points throughout a particular volume alongwith a weighting factor. In various examples, the weighting factor mayreflect, for example, the relative importance, or criticality, ofmeeting or not exceeding the prescription dose at all points in thevolume.

In addition, one or more of the cost terms may include objectiveparameters that determine, at least in part, the value of the costterms, or plan objectives. Free objective parameter values aredetermined during a treatment plan metaoptimization process. In anembodiment, each plan objective is defined as a function of a singlefree parameter. In another embodiment, each plan objective includes asfew free parameters as practicable. Thus, the specific cost functionbecomes a function of the objective parameters.

Before the metaoptimization process is performed, the cost functiongenerator 16 determines an initial value for each of the objectiveparameters. In various embodiments, initial objective parameter valuedetermination is aided by a dose-volume histogram (DVH) estimation modelor another knowledge-based approach.

In an embodiment, at least some of the objective parameters correspondto one or more underlying factors related to the microstate. Themicrostate generally includes all parameters needed to deliver the doseto the patient. The cost function is used to attain a near-optimalmicrostate based on the clinical goals. In general, the metaoptimizationprocess attempts to optimize the free objective parameters such that allof the clinical goals are fulfilled, or such that as many clinical goalsas possible, in order of priority, are fulfilled. As a result, the dosedistribution related to the microstate that minimizes the cost functionbecomes a function of the objective parameters.

The state analyzer 18 determines the microstate that minimizes the valueof the current cost function. In some embodiments, for example, in orderto improve system performance, the selected microstate represents anon-optimal solution for the current cost function. In this case, asolution may be selected based on convergence towards an optimalsolution. For example, in an embodiment, a single iteration orrelatively few iterations are performed using an iterative gradient flowmethod to search for the microscopic state before the objectiveparameters are adjusted.

The dose distribution evaluator 20 determines the dose distributionresulting from the current microstate. For example, the dosedistribution evaluator 20 may create a dose-volume histogram (DVH). Thedose distribution evaluator 20 may implement any dose distributionestimation algorithm known in the art.

The clinical goal assessor 22 evaluates achievement of the clinicalgoals based on the current microstate. For example, the clinical goalassessor 22 analyzes the dose distribution information generated by thedose distribution evaluator 20 to determine whether each of the clinicalgoals has been attained.

The parameter adjuster 24 alters the values of the objective parametersin order to seek a microstate that minimizes the value of the costfunction while producing a near-optimal clinical solution. In anembodiment, the parameter adjuster 24 projects gradients of the costterms corresponding to individual plan objectives to estimateappropriate adjustments to the parameter values in order to construct acost function with a related microscopic state that results in atreatment plan that relatively closely matches the clinical goals. Thegradients represent forces tending to drive the objectives, and thus,the cost function.

For example, the local gradient of a cost term with respect to anobjective parameter may be projected to estimate the parameter value atwhich the associated clinical goal would be marginally achieved. Theresulting parameter value represents an estimated bound regardingmodification of the parameter. In this manner, estimated bounds may bedetermined with regard to various competing objectives.

In an alternative embodiment, the parameter adjuster 24 anticipates dosedistribution reactions to guide the adjustment of the objectiveparameters in the metaoptimization process. In general, any change madeto an objective parameter causes a resultant reaction in the dosedistribution. The reaction response may be extrapolated based on aresponse assumption, for example, assuming a linear response. Theextrapolated response may be used to estimate the required amount ofadjustment to the parameter needed to attain a desired change in thedose distribution, and thus, to meet a specified clinical goal. In asimilar manner, it is possible to estimate the maximum adjustment to theparameter that will not violate another clinical goal.

In the case that it is not possible to simultaneously attain all of theclinical goals, the parameter adjuster 24 takes the specified prioritiesinto account in determining which of the clinical goals to prioritize.For example, the parameter adjuster 24 may require that all planobjectives related to higher-priority clinical goals be met beforeattempting to fulfill a plan objective related to a lower-priorityclinical goal.

Other embodiments are within the scope of the following claims. Forexample, in another implementation, the IMRT treatment planning devicepermits the user to directly specify generalized clinical goals relatedto normal tissue objectives (NTO). Thus, the user may specify, forexample, “no dose larger than accepted to target in the normal tissue,”or “no dose higher than 60% of the target dose level anywhere more than6 centimeters away from the target.”

The specified clinical goals are automatically converted into suitableobjectives controlling the dose distribution in the normal tissue. Forexample, the IMRT treatment planning device designs a spatial objectivethat affects a region wherein all points share a common feature, such as“distance to the closest target is within specified range,” effectivelydefining a shell for the union of the target. Any dose in the regionabove a preset objective dose level, such as slightly below theprescription dose level, cause the corresponding cost term to contributeto the total cost function.

NTO terms also may include more complex metrics, such as those used indose distribution estimation algorithms. During the metaoptimizationprocess, the individual contributions of the NTO terms to the total costfunction are adjusted in order to attain the desired clinical goals. Forexample, the example preset objective dose level and an associatedobjective weight are tuned such that the corresponding clinical goal ismet.

In another implementation, the IMRT treatment planning device canreceive a residual goal and convert it into a suitable plan objective.The residual goal may be only partially attained while aidingconvergence of the metaoptimization process toward a single solution. Anexample residual goal would be to reduce the dose level in a particularset of critical organs. In this case, the residual clinical goal couldbe converted into an objective represented by a constant multiplied bythe dose level.

Another example would be to leave increasing margin around each clinicalgoal, which could be beneficial in situations where the plan qualitymight be reduced in some later treatment planning step, such as whenconverting optimal fluence to leaf sequence or subsequently calculatingthe dose distribution with a more accurate dose calculation algorithm.

In general, a single residual objective is sufficient to aidconvergence, and a clinical counterpart is not strictly required. Inaddition, so long as the desired effect can be directly represented by acost term in the cost function, the residual goal need not be preciselydefined.

The systems described herein can offer advantages such as automaticconversion of specified clinical goals into plan objectives that can beoptimized to produce a near-optimal treatment plan. Embodiments canautomatically create treatment plans that fulfill specifiednormalization criteria, or that do not exceed a specified maximum dosefor a particular organ-at-risk (OAR).

As illustrated in FIG. 2, an exemplary general computing device 30 thatcan be employed in the intensity-modulated radiation therapy (IMRT)treatment planning device 10 of FIG. 1 includes a processor 32, a memory34, an input/output device (I/O) 36 storage 38 and a network interface40. The various components of the computing device 30 are coupled by alocal data link 42, which in various embodiments incorporates, forexample, an address bus, a data bus, a serial bus, a parallel bus, orany combination of these.

The computing device 30 communicates information to and requests inputfrom the user or other devices by way of the I/O 36, which in variousembodiments incorporates, for example, an interactive, menu-driven,visual display-based user interface, or graphical user interface (GUI).The computing device 30 may be coupled to a communication network by wayof the network interface 40, which in various embodiments incorporates,for example, any combination of devices—as well as any associatedsoftware or firmware—configured to couple processor-based systems,including modems, access points, network interface cards, LAN or WANinterfaces, wireless or optical interfaces and the like, along with anyassociated transmission protocols, as may be desired or required by thedesign.

The computing device 30 can be used, for example, to implement thefunctions of the components of the IMRT treatment planning device 10 ofFIG. 1. In various embodiments, the computing device 30 can include, forexample, a server, a controller, a workstation, a mainframe computer,personal computer (PC), a note pad, a computing tablet, a personaldigital assistant (PDA), a smart phone, a wearable device, or the like.Programming code, such as source code, object code or executable code,stored on a computer-readable medium, such as the storage 38 or aperipheral storage component coupled to the computing device 30, can beloaded into the memory 34 and executed by the processor 32 in order toperform the functions of the IMRT treatment planning device 10.

Referring now to FIG. 3, an exemplary process flow is illustrated thatmay be performed, for example, by the IMRT treatment planning device 10of FIG. 1 to implement an embodiment of the method described in thisdisclosure for developing an intensity-modulated radiation therapy(IMRT) treatment plan. The process begins at block 50, where a set ofclinical goals are received regarding an IMRT treatment plan for apatient.

In block 52, as explained above, the clinical goals are converted toplan objectives, for example, dose-volume histogram (DVH)-basedobjectives. Each objective includes at least one free parameter, forexample, a location or a weighting. An initial value is determined foreach parameter in block 54.

A cost function is constructed, in block 56, with cost terms based onthe plan objectives including the current set of objective parameters.In block 58, a search is performed, for example, using a gradient flowanalysis of the cost function, to identify a microstate that results ina reduced or near-minimal value of the current cost function. A set ofdose distributions is calculated, in block 60, as needed to evaluate howwell the current microstate attains the specified clinical goals.

In block 62, the objective parameter values are individually adjusted,as explained above, so as to guide the dose distributions to betterachieve the clinical goals. In block 64, a determination is made as towhether or not a terminal, or stopping, criterion has been met. If so,then the process ends. Otherwise, if the terminal criterion has not beenmet, then the process is repeated from block 56. As such, themetaoptimization process is iteratively carried out until the terminalcriterion has been met.

Aspects of this disclosure are described herein with reference toflowchart illustrations or block diagrams, in which each block or anycombination of blocks can be implemented by computer programinstructions. The instructions may be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to effectuate a machine orarticle of manufacture, and when executed by the processor theinstructions create means for implementing the functions, acts or eventsspecified in each block or combination of blocks in the diagrams.

In this regard, each block in the flowchart or block diagrams maycorrespond to a module, segment, or portion of code that including oneor more executable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functionality associated with any block may occurout of the order noted in the figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, orblocks may sometimes be executed in reverse order.

A person of ordinary skill in the art will appreciate that aspects ofthis disclosure may be embodied as a device, system, method or computerprogram product. Accordingly, aspects of this disclosure, generallyreferred to herein as circuits, modules, components or systems, or thelike, may be embodied in hardware, in software (including firmware,resident software, micro-code, etc.), or in any combination of softwareand hardware, including computer program products embodied in acomputer-readable medium having computer-readable program code embodiedthereon.

It will be understood that various modifications may be made. Forexample, useful results still could be achieved if steps of thedisclosed techniques were performed in a different order, and/or ifcomponents in the disclosed systems were combined in a different mannerand/or replaced or supplemented by other components. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. An apparatus for developing anintensity-modulated radiation therapy treatment plan, the apparatuscomprising: a memory that stores machine instructions; and a processorthat executes the machine instructions to: generate a cost functioncomprising a parameter value based on a plan objective; identify amicrostate that results in a reduced value associated with the costfunction, wherein the reduced value iteratively converges on a resultantvalue of the cost function; adjust a value associated with the parameterto improve a fulfillment level of a clinical goal associated with theplan objective; and generate an intensity-modulated radiation therapytreatment plan based on the resultant value.
 2. The apparatus of claim1, wherein the parameter value comprises a machine parameter value. 3.The apparatus of claim 2, wherein the machine parameter value comprisesat least one of a selected field geometry and a selected monitor unit(MU) limit.
 4. The apparatus of claim 1, wherein the parameter valuecomprises an optimal fluence and wherein the resultant value is aminimum value.
 5. The apparatus of claim 4, wherein the processorfurther executes the machine instructions to convert said optimalfluence to a leaf sequence and to reduce a margin defined by theclinical goal.
 6. The apparatus of claim 1, wherein the processorfurther executes the machine instructions to: estimate an initial valueof the parameter value; and adjust the parameter value by projecting agradient to estimate a goal value at which the clinical goal isachieved.
 7. A method of developing an intensity-modulated radiationtherapy treatment plan, the method comprising: determining a pluralityof plan objectives based on a plurality of clinical goals; generating acost function incorporating the plurality of plan objectives, whereinthe cost function comprises cost terms each comprising a respectiveparameter value corresponding to the plan objectives; determiningpriority levels for the plurality of plan objectives; identifying amicrostate that results in a reduced value associated with the costfunction, wherein the reduced value iteratively converges on a resultantvalue of the cost function; adjusting parameter values of the cost termsbased on to the microstate to improve a respective fulfillment levelassociated with the clinical goals according to the priority levels; andgenerating an intensity-modulated radiation therapy treatment plan basedon the plurality of parameter values.
 8. The method of claim 7, whereinthe value of the cost function equals a sum of the cost terms.
 9. Themethod of claim 8, wherein the cost terms minimize the value of the costfunction when the corresponding plan objectives are attained, andwherein the resultant value of the cost function is a minimum value. 10.The method of claim 7, wherein the adjusting the parameter values of thecost terms comprises projecting a gradient associated with the costterms to estimate a goal value at which the clinical goal is achieved.11. The method of claim 7, wherein the adjusting the parameter values ofthe cost terms comprises estimating a resultant response of a dosedistribution associated with a prospective adjustment of the respectiveparameter value based on an extrapolation corresponding to a localizedresponse of the dose distribution.
 12. The method of claim 7, furthercomprising assigning initial estimates to the plurality of parametervalues based on an estimated dose distribution.
 13. The method of claim7, further comprising receiving the clinical goals as user input. 14.The method of claim 7, wherein the plurality of plan objectives areassociated with a respective dose level corresponding to a point in apatient.
 15. The method of claim 7, wherein the plurality of parametervalues are associated with one selected from the group consisting of: amachine parameter; a selected field geometry; and a selected monitorunit (MU) limit.
 16. A computer program product for developing anintensity-modulated radiation therapy treatment plan, the computerprogram product comprising: a non-transitory, computer-readable storagemedium encoded with instructions adapted to be executed by a processorto implement a method of: determining a plurality of plan objectivesbased on a plurality of clinical goals; generating a cost functionincorporating the plurality of plan objectives, wherein the costfunction comprises cost terms each comprising a respective parametervalue corresponding to the plurality of plan objectives; determiningpriority levels for the plurality of plan objectives; identifying amicrostate that results in a reduced value associated with the costfunction, wherein the reduced value iteratively converges on a resultantvalue of the cost function; adjusting the plurality of parameter valuesbased on to the microstate to improve a respective fulfillment levelassociated with the plurality of clinical goals according to thepriority levels; and generating an intensity-modulated radiation therapytreatment plan based on the plurality of parameter values.
 17. Thecomputer program product of claim 16, wherein the value of the costfunction equals a sum of the cost terms.
 18. The computer programproduct of claim 17, wherein the cost terms minimize the value of thecost function when the corresponding plan objectives are attained, andwherein the resultant value of the cost function is a minimum value. 19.The computer program product of claim 16, wherein the adjusting theplurality of parameter values comprises projecting a gradient associatedwith the cost terms to estimate a goal value at which the clinical goalis achieved.
 20. The computer program product of claim 16, wherein theadjusting the plurality of parameter values comprises estimating aresultant response of a dose distribution associated with a prospectiveadjustment of the respective parameter value based on an extrapolationcorresponding to a localized response of the dose distribution.